The hair cell is the primary mechanoelectrical transducer in auditory and vestibular function, Its unique role is reflected in a shape, ultrastructural apparatus, and physiologic properties unlike those of any other cell. Our understanding of the cell and molecular biology of the hair cell is rudimentary, largely as a result of the difficulty in obtaining sufficient tissue. The long-range goal of the proposed studies is to identify, using a molecular biologic approach, molecules responsible for the particular mechanical, electrical, neurochemical, and regenerative properties which define the function of the hair cell, We will begin to identify these molecules through the use of cDNA libraries which we have constructed from the cochlea of the chick and from the saccular macula of the bluegill sunfish. Candidate hair cell and supporting cell-specific cDNAs will be identified by differential screening and subtractive hybridization techniques using RNA isolated from the hair cell epithelia, from individual hair cells, and from other tissues. cDNAs representing homologues of known molecules of suspected importance in hair cell function will be identified by screening of the libraries with existing probes. The cellular and tissue specificities of identified cDNAs will be confirmed by northern blots and in situ analyses, and selected clones will be sequenced and further characterized. The identification of proteins which are responsible for the remarkable functioning of the hair cell should help us understand, in molecular terms, how this cell manages to respond in such a sensitive and precise manner. The identification of such molecules should provide a starting point for more directed searches for the molecular substrates of hearing and vestibular disorders.